Joining abrasive articles



' Sept. 13, 1932.

FHLTONE JOINING ABRASIVE ARTICLES Filed Feb. 13, 1929 as illustrated comprises two thin layers of metal 5 and 6 applied into intimate contact with the surfaces of the abrasive blocks, and

an intermediate layer 7 ofa low melting point.

metal which is poured in and wets the metal facings 5 and 6. The abrasive segments or blocks may be of any suitable abrasive material, preferably molded blocks of artifi ci ally bonded abrasive having a high melting point bond. Examples of such abrasives are silicon carbide or aluminum oxide bonded by ceramic bonds vitrified at high temperatures. Such abrasivematerials may have a tensile strength of 1,000 or more pounds per square 111C The surfaces of the abrasive blocks are somewhat porous, showing fine pits between the abrasive grains and thus offering a good anchorage for the metal coating which is sprayed on.-

The surfaces of the abrasive segments which are to be joined are first freed from dust and foreign particles by means of an air blast. They are then sprayed with molten metal, such as brass, to form the thin metal coatings 5 and 6 on the abrasive surfaces. The abrasive segments may be sprayed cold or may be heated preparatory to spraying. Devices for applying metal coatings by themolten spray process are well-known and do not need to be described in detail. See, for example, the book on Metal Spraying by Turner and Budgen, London, 1926, or article on Metal Coating by Spraying Process in Handbook Encyclopedia of Engineering, New York, 1928. Usually the metal spray is produced by means of a metal wire which is fed through the nozzle of an oxy-acetylene torch. The metal is fused to a high temperature by the flame and is then carried b a high velocity stream of compressed air against the surface to be sprayed.

The sprayed metal is driven into the pores of the surface and into adherent contact therewith so as to wet or give the effect of wetting the surfaces of the abrasive segments. The coating of metal thus applied to the abrasive surface adheres to it strongly.

I have found that brass is a satisfactory metal to be sprayed in molten condition against the abrasive, since it wets or gives the effect of wetting the surface. Other then in condition to be assembled in the wheel. It is, however, not necessary to follow the above procedure before assembling the segments into a wheel.

The segments are then assembled into wheel form, such as shown in Figuresj2 and 3, by means of suitable assembling clamps and supports. In assembling the wheel small spacers are put between the segments so as to leave spaces between the adjacent metal s rayed surfaces to receive themetal which 1s cast into such spaces to form the joints. For example, as indicated in F igure 1, a small spacer or shim 8 may be put between the outside edges of the segments 2 and 3 to space them apart. Similar spacers will be placed between the inner edges of the segments in assembling the wheel. After the wheel is thus assembled, it is put into an oven at a temperature of about 300 Fahrenheit, which is then gradually increased to about 425 Fahrenheit in three or four hours. Solder or other suitable low melting point metal or alloy is then poured in between the metal-coated surfaces of the segments and the wheel is allowed to cool gradually. This solder is indicated at 7 in Figure 1. The edges of the oints to be filled with the metal are, of course, suitably stopped so as to retain the molten metal.

The solder or other metal wets the brass or coating metal so as to form a tensilely strong joint between the abrasive segments.

The bond or adherence between the metal joint thus formed and the abrasive surfaces is comparable in strength to the tensile strength of the abrasive material itself.

After the wheel is cooled down the spacers, such as those indicated at 8, are removed. The cavities left by the spacers may be filled with solder or other metal, or where the cavities leftby the removal of the spacers are at the exterior of the wheel, the surface of-the wheel may be dressed down to obliterate such cavities and form a continuous cylindrical.

surface. I

The metal used for casting between the metal sprayed surfaces may be of any suitable low melting pointmetal, such as solder, lead, lead-tin, lead-bismuth, etc.

In Figures 2, 3 and 4 is illustrated a pulp wheel embodying the invention. The wheel is built up of a number of segments, indicated by reference numerals 10, which are joined together by the strong hot water resisting joints 11, preferably formed as above described. The wheel is assembled as shown in Figures 2 and 3. In Figure 4 the wheel is shown as mounted on a suitable driving arbor or shaft 12 by means of end clamping plates 13 and 14. I

Since the joints formed between the segments have a strength approximating that of the bonded abrasive, and since such joints retain their strength under working conditions, reliance may be placed upon the structural strength of such joints, and the elaborate precautions employed for securing the segments to a central drum or arbor in making pulp wheels which do not have such strong joints, may be obviated, thus reducing the cost of the wheel. So far as the strength of the wheel is concerned, a segmental wheel thus built up and formed is comparable to one of monolithic structure.

Tests have been made as to the strength of the metal joints formed, as above described, between sections of artificially bonded abrasive material. The metal joints showed initially a tensile strength of about 1,000 pounds per square inch, which is approximately that of the abrasive material itself. It was found that subjecting the joints to boiling water for prolonged periods did not decrease this strength. The strength of the metals inthe joint is, of course, unafiected by the hot water, and the character of juncture between the metal and abrasive is such as to also be substantially unaffected by the hot water.

The joints of the character above described differ from those formed by merely pouring in a metal, such as solder or lead, between abrasive segments, in that such poured-in metal does not adhere strongly to the surface of the abrasive, as does the sprayed-on coating. The sprayed-on coating either Wets or gives the effect of wetting the abrasive grains. The hot water, even containing the matters extracted from the ulp, finds nothing which it can attack or issolve or emulsify in the metal joint as thus applied, thus differing from the joints formed from the phenol condensation product resins heretofore suggested for this purpose.

In forming the abrasive segments they are usually formed by tam ing or pressing in shaping molds. The e ect of so molding is to cause the outer skin of the segment in contact with the face of the mold to be somewhat more dense, compact and stronger than the interior of the segment. The composite joints formed of the sprayed-on and cast-in metal are therefore bonded with the strongest part of the segments and form, in effect, a supporting spider which strengthens the wheel. A wheel of this character formed of the built-up segments with such supporting strengthening spider may actually be safer and stronger than would be a monolithic wheel. Moreover, since the joints are unaf fected by the hot water, the strength of the wheel is not affected by its use in pulp grind-' ing. a

The metal joints as above described may be properly spoken of as cementitious joints since they serve to cement-or secure the abrasive segments together against tensile forces, as contrasted with metal poured between the segments serving merely as a filler to fill up the inter-segment crevices. 1

. I do not wish to limit myself as to the abrasive material. While the test-pieces re ferred to above are constituted mainly of fused alumina, I have made test wheels from bonded abrasivesegments which were joined together with a form of joint resistant to boiling water. a a

While I have specifically illustrated and described the preferred embodiment of my invention, the invention is not so limited but may be otherwise embodied and practiced Within the scope of the following claims. I claim: V Y 1. The method of uniting preformed blocks of abrasive material, which comprises spraying molten metal onto the faces to be uni-ted so as to form metal coatings firmly adherent to such surfaces, and uniting such metalcoated surfaces by metal cast between them and wetting and adhering to the metal coatings and while maintaining the metal coatings at a temperature below the temperature at which the metal flows.

2. The method of joining blocks of abrasive material, which comprises spraying molten metal against the surfaces. to be united so as to form tightly adherent metal coatings thereon, heating the blocks, applying flux to the surfaces, dipping the surfaces in a low melting point metal, assembling the blocks to leave casting spaces between the thus metal-coated surfaces, and casting a low melting point metal into such spaces.

3. The method of making abrasive wheels for pulp grinding and the like, comprising forming a plurality of segments of abrasive material, spraying the surfaces of the segments to be united with molten brass so as to form tightly adherent brass coatings thereon, heating the segments to a temperature below the melting point of solder, and applying flux to the brass surfaces, coating the brass surfaces with a thin layer of solder, assembling the segments leaving crevices between the thus-coated surfaces, heating the thus-assembled wheel, and pouring molten solder into the crevices.

4. The method of joining molded abrasive blocks which comprises the steps of spraying the surfaces of the blocks to be joined with molten metal to force the metal into the surface pores of the abrasive blocks and thereby form adhering layers of metal on the surfeces of the bloclrs -o be joined, and thereafter joining "she bleclrs by applying 9. second; metal between tlie'metellic coaied surfaces of the blocks, which second metal melts at e iemperature belew the t iiiperacwre t which the metal coatings melt and which when melted adheres in the first metal coat Lines,

The method of joining two preformed abrasive blocks which comprises spraying molten brass against the surfaces of the blocks to be joined, and thereafter soldering the brass coated surfaces together,

(3. An abrasive Wheel consisting of a, pine relity of preformed abrasive blocks connected by bi-rnetellic joints, each of said joints comprisinglayers of higher melting point metal on the blocks and interlocked with said blocks of brass, each of said layers of brass being attached to an abrasive block by prejectens of the brass interlocking with the pores 0i ihebloclz.

In 'est-imony whereof l have hereunie see my bend.

FRAIIK J, TUNE" essences "I, All abrasive Wheel censistiiig of e plu- 

